At ISO 400 the situation is almost reversed - the SD500's stronger noise reduction has started to seriously affect overall sharpness, whereas the Nikon image - though noisier - has retained virtually all the detail (and actually looks sharper than the ISO 50 image: the 7900 uses dynamic 'auto sharpening' by default). In fact this is one of the better ISO 400 images we've seen from any camera using this latest generation 7MP chip. It's nice to see that Nikon's noise reduction system is removing chroma noise, leaving only grain-like luminance noise and lots of detail.